> Can you tell from a fossil anything about the loop of Henle? When we > returned to the land maybe our loops of Henle shortened again, but were > longer in the aquatic ape.

Soft tissue features are not present in any fossil hominoid so it is
impossible to determine the length of the loop of Henle. Given that
however, we can get a good approximation by looking at the distribution
of this character among other primates and within human populations.
There is actually very little variation present, even for those
primates that might benefit by increased water conservation (the
ultimate function of the length of the loop). Given this distribution,
you must assume that the putative aquatic ape aquired said long loop and
then lost it completely (thus obscuring any data). Is this reasonable?
Most scientist would say that it is not, it is certainly not
parsimonious. Furthermore, humans that live in deserts and presumably
would want to have decreased amounts of water in their urine do not have
marked differences (aboriginal populations have been isolated in dry
environments for at least 30k years). Given that there is no variation
in those populations is it reasonable that humans have lost such a
usefull adaptation? I do not think so.